The objective of the Design and Analysis (D&A) Core is to effectively support the scientific goals of this Rett Center Program Project. This Core is an outgrowth of the Data Management Core created in the original Rett Center Program Project. The change in name is to emphasize the collaborative involvement of D&A Core members in all aspects of a study from (step 1) initial developmental discussions to (step 2) development of a formal protocol, to (step 3) design and field testing of data collection forms, to (step 4) development of a database management system, to (step 5) overseeing the entry of the data, to (step 6) analysis of the data in collaboration with the study investigators, to (step 7) collaborating on the development of a manuscript, and if appropriate, to (step 8) collaborating on the development of a grant proposal to support the next stage in development of the study. In addition, the core will continue the creation of a flexible Master Database that will allow for fast retrieval of any segment of the data be it from a single project or multiple projects, that will allow for the addition of new projects or new variables for ongoing projects and that will include quality control and security features that will guarantee that the Rett Center data is of high quality. The Core will continue to expand an online readily accessible system (with a supplementary paper report for those who prefer that medium) that keeps Rett Center investigators informed as to the demographic, clinical and pathological aspects of patients in the Rett Center Master Database. Only basic data will be available online but listings of the type of other data that has been collected will be available as will a list of protocols the patients are currently on. In collaboration with investigators from the Survival Study, the core will develop and maintain the hardware and software necessary to establish and maintain a national clinical database and electronic network that will stimulate and support collaborative, multi- center longitudinal studies in Rett Syndrome.